Dental caries is the single most common chronic childhood disease. Each year, more than 51 million school hours are lost due to dental-related illness and over $40 billion is spent on the treatment of this disease. Epidemiological and clinical studies have suggested that mutans streptococci, particularly Streptococcus mutans, are the major microbial pathogens associated with dental caries. The most commonly used technique to identify S. mutans is cultivation on selective media. The major limitations of the method include inadequate detection of S. mutans in saliva particularly when S. mutans is present at low levels; morphology varies depending upon the medium used; and it is costly and labor-intensive. To date, the most reliable technique to rapidly and specifically identify bacterial species is PCR. But for S. mutans, the lack of species-specific probes and primers continues to limit high-throughput research on prevalence and colonization of S. mutans. Therefore, the objective of this project is to develop highly sensitive and species-specific probes and primers that can be used in PCR-based assays to rapidly, accurately, and effectively identify S. mutans in clinical oral specimens. Our goal will be accomplished by pursuing the following specific aims. (1) To identify potentially unique sequences in S. mutans genome that will enable us to develop species-specific probes and primers for the detection of S. mutans in the clinical specimens. (2) To validate the probes and to demonstrate the high sensitivity and specificity of the species-specific probes and primers. (3) To compare the species-specific probes and primers with the conventional culture method. From these experiments, we should be able to obtain well-defined S. mutans-specific probes and primers and to prove the superiority of the newly developed probes to the findings obtained from the culture method. The new molecular markers will enable us to conduct molecular epidemiological studies of S. mutans infection and high-throughput research so that we can improve our understanding of the polymicrobial etiology of dental caries, ascertain a child's risk potential prior to disease development, and evaluate the effectiveness of caries interventions. Application of the new molecular tools will have a substantial impact on improving the oral health of children.